Hello,
The soluction is to force the encode, your code must be like this:
BEGIN:VCARD
VERSION:4.0
N;CHARSET=utf-8:T€st;Björn
ORG:ÖÜÄ
TEL;CELL:+12 (34) 567890
ADR;CHARSET=utf-8:;;Blà St.;Blè Town;;12345;ç-Land
URL:https://www.test123.com
EMAIL;WORK;INTERNET:mailexample
END:VCARD
I hope that it solve your issue